This invention relates in general to electrical connectors. More specifically, it relates to a hybrid electrical-pneumatic connector between (i) a gas flow and a high current, high voltage, high frequency power supply and (ii) a plasma arc torch.
Plasma arc torches for welding and cutting metal require high D.C. currents during normal piercing, cutting or welding operations, e.g. 20 to 1,000 amperes, but they also require high voltages at a high frequency to initiate the arc on start up A typical voltage is 5 KV and typical high frequencies are 2 to 3 mHz. The arc also requires a supply of a gas that can be ionized to form the plasma arc.
A problem inherent in these operating conditions is that the high voltage, high frequencies conducive to producing an arc at the torch will also produce an arc between the electrical power conductor of a connector and any nearby metal such as another conductor or the housing. Along any possible clear air path between metal and the current carrying conductor must be maintained above a minimum value for this "tracking distance" to avoid arcing. If an arc occurs upon application of the high frequency, high voltage, then when the large direct current begins, this current will shorted-out and destroy the connector because the high D.C. current follows the arc.
Other problems are that any connection arrangement must also supply the gas, must have large electrical conductors sized to carry the large currents, and the connector system must be able to dissipate the heat produced by the resistance heating of the heavy currents. The heat dissipation is particularly important if the connector includes multiple high current conductors. Heat dissipation problems often control the design and size of a connector in such a system. In general, known multiple conductor, high current connectors are large.
The current standard industry practice is to connect the power and gas supplies to the plasma arc torch using leads, often 25 or 50 feet in length, that are connected inside the power supply permanently. In the leads it has been adequate to place the electrical conductor in an insulating, gas-carrying tube. This arrangement, however, does not allow a quick disconnect, and it is not satisfactory for the connection at the power supply. Whenever the power supply or torch is changed, or whenever the system is moved or shipped, a licensed electrician must be called to open the power supply and disconnect, connect or change the leads. Changing torches or power supplies therefore becomes a cumbersome, time-consuming task. There is clearly a great advantage to being able to disconnect the leads quickly, without the services of a specially trained individual, but no connection system currently available meets all of the aforementioned requirements while also providing a quick connect and disconnect in the field.
Of course, a wide variety of plug-type electrical connectors are known for use in other applications, and a few replaceable, quick connect/disconnect connectors are known for use with plasma arc torches. However, they all have disadvantages which limit their value as solutions to all of the competing design objectives delineated above. One connector used in conjunction with a plasma torch, at least in Europe, connects both the gas and power supplies to the torch, but the electrical power is limited to a high current only. High voltages at a high frequency are simply not put through this connector. It therefore is of limited value. Another connector for use with a plasma torch, also known at least in Europe, is a large, conventional design plug and receptacle electrical connector. It does convey a gas through passages in the conductors, but the conductors are large in cross section, comparable to the AWG size of standard conductors used to carry the same current. The conductors are also spaced within the connector in a conventional manner. As a result, this connector is quite large and therefore difficult to manipulate, costly to manufacture, and it requires a relatively large force to insert the plug into the receptacle to make a connection. The insertion problem is due in part to the stiffness of the resilient components and in part to the difficulty in achieving a good alignment of the mating components as they are manually aligned and forced together. None of the known connectors supply gas and electrical power (both at high D.C. current levels and at high voltage (5 KV) and high frequency) while controlling arcing in the connector, controlling gas leakage, and allowing a quick, reliable connect or disconnect with no special skills.
It is therefore a principal object of the present invention to provide a hybrid gas and electrical power that carries power at both high D.C. current levels and at high voltages and high frequencies which can be connected and disconnected quickly and with a low skill level.
It is a further object to provide a connector with the foregoing advantages that is compact as compared to comparably rated conventional electrical connectors.
Another object is to provide a connector with the foregoing advantages that has good heat dissipation characteristics and a low insertion force as compared to comparably rated conventional electrical connectors.
A further object is to provide a connector with the foregoing advantages that also reliably seals the gas flow within the connector.
Yet another object is to provide a connector with the foregoing advantages that control arcing.
Still another advantage is to provide a connector with the foregoing advantages that allows a flexibility in manufacture to meet a range of applications utilizing the same basic construction.
Another object of the present invention is to provide a connector with the foregoing advantages that is reliable in its operation and which has a favorable cost of manufacture